The present invention relates to a method and apparatus for the non-destructive, on-site assessment of the performance of resilient elastic substrates. In particular, the present invention relates to the assessment of, for example, sealants on building facades.
For convenience, the background of the invention will be discussed with reference to a particularly suitable field of application of the method and apparatus of the inventionxe2x80x94the assessment of sealants. Corresponding art for other resilient elastic substrates will be readily determined by those skilled in the art.
The predisposition for all year round air-conditioning and the ever increasing energy cost, coupled with the high level of prefabrication in construction, have increased the role played by sealants in building joints. Effective sealants are important in contributing to successful watertight building envelopes and preventing infiltration of air. The high cost of energy for air-conditioning and problems associated with water infiltration are rendering the serious consideration of building sealants essential. The long term financial impact of poor sealants on the cost of keeping the building comfortable is now also being calculated by building owners.
Sealants have conventionally been widely used in building and civil engineering works as they serve several general functions as follows:
(a) Waterproofing Function
Sealants are used as components of complete waterproofing system by resisting the passage of water into the jointing part of the building.
(b) Environmental function
Sealants are used as barriers to resist the passage of heat, light, sound, odour, dust, etc. into the building.
(c) Movement Control Function
Sealants are used to accommodate continuing changes in size of the joint due to thermal, moisture and structural movements, including vibration and creep.
A sealant must be able to perform these functions, and at the same time it must have acceptable appearance and durability, be economically acceptable, and have acceptable maintenance costs. In some cases, additional functions may also be required such as ability to perform under special temperature or humidity conditions and ability to withstand polluted atmosphere.
The performance of sealants depends to a large extent on the proper selection according to the environment to which the sealant is to be exposed, and is influenced by the workmanship and methods of application on site. Sealants are generally expensive to install and remove, and thus replacement costs may be high even though the sealant itself as a material may be relatively inexpensive.
In recent years, the deterioration of sealants has attracted much attention in conjunction with the construction industry""s increasing use of large panel curtain walls. Many sealants in high rise buildings are reaching the limit of their life span. To derive an efficient repair/maintenance strategy for a large area such as in the case of a building facade, an efficient on-site non-destructive diagnostic technique is essential. Temporary work in the diagnostic process must be minimised. At present, no such scientific method is available. The conventional techniques are generally based on tedious, destructive, slow laboratory based methodologies.
In the case of determining the durability and performance of new sealants, the conventional testing techniques generally stipulates that the sealant must be statically cured for a period of 28 days before the tests are to be conducted. This seems to suggest that the accentuation when it comes to selection of suitable sealants for a particular job is on how it will perform under weathering, ignoring the fact that failure may actually occur before the sealant has a chance to cure. In practice, sealants which are installed on-site, do not xe2x80x9cenjoyxe2x80x9d the luxury of being statically cured in a fixed position, before experiencing undue stress caused by movements. They are subjected to dynamic curing rather than static curing and occurrences of premature failures are highly possible. This highlights the concern that conventional control tests conducted may be meaningless if sealants were to fail before they are put to service. It is thus important to monitor the in-service performance of sealants regularly especially during the initial stage after application. To achieve that, a reliable on-site, non-destructive diagnostic technique is needed.
The present invention advantageously provides a method and apparatus for the accurate, quick and non-destructive, assessment of the performance of resilient elastic substrates, such as sealants, for example on building facades, on-site. It is envisaged that such a method and apparatus may be applicable in the fields of maintenance and repair of building facades, performance assessment and diagnosis, and quality control in manufacturing and on-site applications.
According to one aspect of the invention there is provided a method for the non-destructive, in-situ assessment of a resilient elastic substrate, the method comprising the steps of:
applying detector means to a surface of the substrate;
urging the detector means into the substrate at a substantially constant speed to a predetermined depth;
holding the detector means at the predetermined depth for a predetermined time;
releasing the detector means, allowing elastic recovery of the substrate; and
processing compressibility and/or elastic recovery of the substrate during the urging, holding and/or releasing steps.
The application of the detector means to the surface of the substrate, urging of the detector means into the substrate, holding of the detector means at the predetermined depth, and releasing of the detector means may be manually or automatically controlled. Furthermore, the speed at which the detector means is urged to the predetermined depth, the predetermined depth and the predetermined time may be determined based on the particular substrate being assessed. However, in a preferred embodiment the detector means is urged into the substrate at a speed of from about 0.3 to about 0.7 mm/s, more preferably at a constant speed of about 0.5 mm/s. Further, it is preferred that the detector means be held at the predetermined depth for a period of at least about 5 seconds. The predetermined depth will generally be no more than about 10 mm, and is preferably about 5 mm.
According to a preferred embodiment, the releasing step comprises maintaining the detector means in engagement with the surface of the substrate for a period of about 5 seconds or more after the release and during elastic recovery of the substrate. The maintaining of engagement of the detector means for at least 5 seconds during elastic recovery of the substrate advantageously enables the attainment of the most representative recovery values for the substrate. That is, the rate of change (i.e. change in elastic recovery with time) within the first 5 seconds after the release of the detector means is the most relevant to the assessment of the performance of the substrate. It will be readily understood that in some cases the rate of recovery after 5 seconds, such as within about 2 hours after the compression of the substrate, may be of interest. Such instances are also envisaged within the scope of the present invention.
While the assessment of the substrate by the above method may provide sufficient information to accurately and efficiently assess the performance of the substrate, further assessment may be made by other means. For example, in one embodiment the method further comprises, on the removal of the detector means from the surface of the substrate, visually inspecting the surface of the substrate to which the detector means has been applied. A detailed visual examination during testing may also be facilitated in order to monitor adhesion and cohesion of the substrate.
According to another aspect of the invention there is provided an elastic recovery testing assembly for the non-destructive, in-situ assessment of a resilient elastic substrate, said assembly comprising:
detector means adapted to be applied to a surface of said substrate and urged into said substrate at a substantially constant speed and held in said substrate at a predetermined depth for a predetermined time;
actuating means for actuating said urging of said detector means into said substrate; and
processing means for storing and/or processing compressibility and/or elastic recovery of said substrate.
Once again, the speed at which the detector means is urged into the substrate, the predetermined depth and the predetermined time may be determined based on the substrate being assessed. Furthermore, the application of the detector means to the substrate, including the urging of the detector means into the substrate, and holding of the detector means in contact with the substrate may be manually or automatically controlled. In a preferred embodiment, the detector means is adapted to be urged into the substrate at a substantially constant speed of from about 0.3 to about 0.7 mm/s, more preferably about 0.5 mm/s. The detector means is also preferably adapted to be held in the substrate at a depth of no more than about 10 mm, preferably about 5 mm.
After the detector means has been held at the predetermined depth for the predetermined time, the actuating means may automatically disengage the detector means, or may be manually disengageable. In any event, the actuating means is preferably disengageable such that, in use when the actuating means is disengaged, the detector means is displaceable by the substrate due to elastic recovery of the substrate. In this instance, as discussed in accordance with the method of the invention above, the detector means is preferably maintained in contact with the surface of the substrate for a period of at least about 5 seconds after the actuating means is disengaged so that recovery values may be attained to facilitate an accurate assessment of the performance of the substrate.
According to a preferred embodiment, the assembly further comprises visual assessment means for facilitating visual assessment of the surface of the substrate to which the detector means has been applied. Advantageously, the visual assessment means may also be used for a detailed visual examination of the surface during testing. Preferably, the visual assessment means comprises a microscope unit mounted on the assembly.
The detector means may comprise any suitable means for application to the surface of the substrate. However, in a preferred embodiment the detector means comprises a detector head which contacts the surface of the substrate, and a piston shaft adapted to be engaged by the actuating means and for urging the detector head into the substrate. More preferably, the detector head is a brass pellet having a width of about 4 millimeters or more. It will be readily understood that the width of the detector head will be determined based on the particular application of the assembly. For example, if the assembly is being used to test a sealant in the joint of a building facade, the detector head will be of a width which may be suitably applied taking into consideration the width of the joint of the facade.
Similarly, the actuating means may comprise any suitable form which may be manually or automatically operable by a user of the assembly. According to one embodiment the actuating means comprises a piston load controller which is manually operable by a user of the assembly to urge the detector means into the substrate.
If the assembly is manually operable, it is preferred that the assembly further comprise prompting means for prompting a user of the assembly. For example, the prompting means may prompt a user of the assembly to increase or decrease the speed at which the detector means is being urged into the substrate. The prompting means may also prompt a user of the assembly to hold the detector means at the predetermined depth, release the detector means to allow the elastic recovery of the substrate, and/or maintain the detector means in contact with the surface of the substrate during elastic recovery of the substrate. The prompting means may comprise any suitable prompt for said user. This may, for example, be a visual or audio prompt. Preferably, the prompting means comprises an electronic display.
The processing of data during use of the assembly may be achieved by any suitable means. Furthermore, data may be simply stored by the assembly for later interpretation using, for example, a computer interface. Preferably, the processing means comprises an electronic transducer or potentiometer which engages the detector means and a load cell which allow instantaneous detection of compressibility and/or elastic recovery of the substrate. As such, in use the assembly advantageously provides a readout which may be recorded and/or interpreted by a user of the assembly. Advantageously the assembly facilitates interfacing with a printer, computer or data logger for detailed data logging of compressibility and/or elastic recovery of the substrate.
The assembly is advantageously a small, light, portable instrument designed for non-destructive, in-situ measurements of the performance of, for example, sealants based on elastic recovery and compressibility.